Currently, trifunctional silanes are mainly used as raw materials for silane-based coating agents which are commercially available and polysiloxanes having moderate hardness and flexibility are formed using such trifunctional silanes. However, hard coatability is still insufficient with the film formed of trifunctional silanes and although colloidal silica or tetrafunctional silanes are mixed with the trifunctional silanes as a supplement, hardening of the films leads to cracking occurring easily and impairment in adhesive properties thereof, which is a problem.
As a silane-based coating agent, for example, a composition for forming antifouling films containing a trifunctional alkoxysilane compound having an epoxy group is known (refer to Patent document 1). Moreover, a silane-based coating agent which contains a photocatalyst is also proposed and films are hardened by using a photoacid generating agent, crosslinking agent, curing catalyst, or the like (for example, refer to Patent documents 2 and 3). Furthermore, a graded material of organic/inorganic composites based on silane having a component-gradient structure in which the content of metal-based compounds in the material changes continuously from the material surface in the depth direction is also proposed (for example, refer to Patent document 4).
[Patent document 1] Japanese Unexamined Patent Application, First Publication No. Hei 10-195417
[Patent document 2] Japanese Laid-Open Patent Application No. 2002-363494
[Patent document 3] Japanese Laid-Open Patent Application No. 2000-169755
[Patent document 4] Japanese Laid-Open Patent Application No. 2000-336281